In previous worl< under this grant, we discovered that inflammatory cytol<ines provide a 'third signal' that determines whether antigen recognition by naive CDS T cells leads to tolerance or full activation and memory, with IL-12 and Type I IFN being the critical cytokines. More recent work has shown that early autocrine production of IFNy can signal for some limited differentiation of naive CD8 T cells so that they develop weak effector functions but do not survive long term. We have also obtained evidence showing that the potential for inhibitory receptors (PD-1) to tolerize CDS T cells by 'exhaustion' differs depending on whether the cells initially responded in the presence of IL-12 or Type I IFN. Based on these findings, we now plan to study the roles of self-antigen-specific CDS T cells in the development of Type I autoimmune diabetes in the non-obese diabetic (NOD) mouse model. We will examine the hypothesis that short-lived, weak effector CDS T cells that differentiate in response to IFNy play a critical role in initiating diabetes by making Ag available to activate CD4 T-helper cells. We will also examine the hypothesis that, upon activation, CD4 T-helper cells will stimulate dendritic cells to produce IL-12 and/or Type I IFN to support development of a strong, long-lived effector CDS response that causes disease and the hypothesis that effector CDS T cells may differ in their diabetogenic potential due to differing levels of PD-1 expression depending on which signal 3 cytokine drives their differentiation. In addition, preliminary evidence suggests that CDS T cells of NOD mice may, in comparison to other strains, have a decreased dependence on a third signal from IL-12 or Type I IFN to undergo differentiation leading to strong effector functions. The possibility that this may contribute to the loss of tolerance to self-antigen in NOD mice will be studied. We anticipate that our planned studies will lead to a better understanding of the mechanisms by which CDS T cell tolerance to self-antigen is lost to result in the development of Type I autoimmune diabetes; information that will likely have application tb development of immunotherapies for prevention and therapy of autoimmunity. RELEVANCE (See instructions): This project examines mechanisms of tolerance induction versus activation of self-antigen-specific CDS T cells in autoimmune disease. Innovative technologies developed by this Program will be used to explore novel concepts regarding the roles of CDS T cells in diabetes, and the findings will contribute to development of better approaches for preventing or treating autoimmune diseases.